I have tried this morning and still couldn’t get the Mac and the iPad to speak to each other.

You mention that the authorisation credentials being the same and I checked that thy had the same email address and password. However when I looked under Help - Authorisation Information it gives a previous email address (which I do still have open) and says this is the default account.

I haven’t yet worked out how to get round it. I would happily erase the default but don’t know how.